poj-3522-Slim Span-kruskal活用

#include <iostream>
#include<algorithm>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<queue>
#include<stack>
#include<math.h>
using namespace std;
#define maxm 110*110
#define maxn 110
#define eps 0.000001
#define zero(x) ((fabs(x)<eps?0:x))
#define INF 99999999
struct list
{
    int u;
    int v;
    int w;
    friend bool operator < (const list &a,const list &b)
    {
        return a.w<b.w;
    }
}edge[maxm];
int f[maxn];
int find(int x)
{
    while(x!=f[x])x=f[x];
    return x;
}
int main()
{
    int n,m,i,j,k;
    while(~scanf("%d%d",&n,&m)&&(n||m))
    {
        for(i=1;i<=m;i++)
        {
            scanf("%d%d%d",&edge[i].u,&edge[i].v,&edge[i].w);
        }
        sort(edge+1,edge+m+1);
        int minn=INF;
        for(k=1;k<=m;k++)
        {
            for(i=1;i<=n;i++)f[i]=i;
            int l=0;
            int amin,amax;
            amin=INF;
            amax=-1;
            for(i=k;i<=m;i++)
            {
                int a=find(edge[i].u);
                int b=find(edge[i].v);
                if(a==b)continue;
                l++;
                amin=min(amin,edge[i].w);
                amax=max(amax,edge[i].w);
                f[a]=b;
                if(l==n-1)break;
            }
            if(l!=n-1)break;
            minn=min(minn,amax-amin);
        }
        if(minn==INF)cout<<"-1"<<endl;
        else cout<<minn<<endl;
    }
    return 0;
}